The Behaviour of Quantum Systems in Strong Fields

Konstantin N. Drabovich, Ludmila S. Kancheva

A. Melikyan

The behaviour of a multilevel system in a strong field is considered, when the interaction energy is much greater than the energy of one quantum and the latter is of the same order as the level spacing of the system. In the case of a monochromatic field the zero-order approximation for quasi-energy is found to be the diagonal matrix element of the unperturbed hamiltonian over the interaction operator eigenfunctions. The asymptotes to the quasi-energy spectrum for the hamiltonian with arbitrary periodic time dependence are also obtained.

Jan Dereziński, Christian Gérard

Nick Huggett, Robert Weingard

Dima E. Feldman

The zero-temperature critical behaviours of the classical Heisenberg and XY ferromagnets in the uniaxial random field are studied in the arbitrary spatial dimension. Exact results are obtained for the magnetization, transversal to the random field direction, at the Gaussian and bimodal distributions of the random field. For the Gaussian distribution the critical behaviour in strong random fields is independent of the spatial dimension. The transversal magnetization, , where is the distribution width. For the bimodal distribution of the random field, the transversal magnetization obeys the law , where is a critical field, and H is the random field amplitude. The same critical behaviour is expected for related systems, for example random antiferromagnets in the uniform field.